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How Do Safety PLCs and Standard PLCs Differ?

How Do Safety PLCs and Standard PLCs Differ?

There are two major programmable logic controllers (PLCs): standard PLCs and safety PLCs, each with their own major functionality and use when it comes to automation. In the world of automation, there are tons of choices, and when efficiency and safety are on the line, making the right choice is critical.

The Basics of Standard PLCs

All standard PLCs do the same thing: automate and control one or more machine processes, including:

  • Timing
  • Control
  • Sequencing
  • Starting and stopping motors, pumps valves and other machine components

PLCs are used to automate an entire system efficiently and without human interaction, save for when an issue arises.

The Basics of Safety PLCs

Safety PLCs have the same basic function as standard PLCs, they operate in the same way, with one major difference: they are specially designed to meet several safety directives:

  • IEC 62061
  • ISO 13849-1
  • IEC 61058

Safety PLCs control all the same machine components as standard PLCs. The main difference is they can have integrated safety functions that also allow it to control safety systems and equipment. They create redundancy and are designed not to fail. If they do fail, they are designed to fail in predictable ways, allowing operators to solve issues quickly. They also contain built in diagnostic capabilities that allows it to monitor inputs and outputs. If something goes wrong, the PLC will automatically and safely shut down.

Safety PLCs have an extra bit of hardware in the form of a safety circuit between the output and the connected device, allowing the PLC to limit damage to external devices in the event of a malfunction.

When Do You Need a Safety PLC?

This depends on the safety standards that regulate your country and the industry in which you manufacture goods for. Food and beverage manufacturers tend to have stricter regulations than other industries, so make sure you understand the safety requirements for your application.

Safety PLCs can also be used to eliminate the need for safety relays, which can save money on the additional parts for the application as well as the time it takes to wire them. Systems that are built around safety PLCs are also more flexible and easier to modify. This is because the system only requires programming changes, not hardware and wiring changes.

Are There Any Disadvantages to Using a Safety PLC?

That depends on your definition of disadvantage. Safety PLCs can save you money over time, but they tend to have higher startup costs. This makes them not as ideal for smaller applications that may get simple use of a safety relay that controls a light curtain and stop button, for example. It depends entirely on the application you are working with and the automation requirements you have.


No Matter Which PLC You Choose, The Right Choice Involves Working with the Right Supplier. AMMC Has All the PLC Products You Need to Optimize Your Automation Process.

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